The laying of flexible tubular conduits subsea is usually preformed from a suitable pipe-laying/pipelay vessel such as a floating platform, barge, ship or other vessel. The flexible tubular conduit may be one of many different forms. The flexible tubular conduit is preferably a flexible pipe of the unbounded type for conveying hydrocarbons as defined in the American Petroleum Institute Recommendations API17J “Specification for unbounded flexible tubular conduit”. However, the flexible tubular conduit may be of the bonded type. The flexible tubular conduit may alternatively be an umbilical as defined in the American Petroleum Institute API17E “Specification for subsea umbilical” third Edition, 2003. Alternatively, the flexible tubular conduit may be an Integrated Production Bundle (IPB) described in the U.S. Pat. No. 6,102,077 and marketed by the applicant under the registered trademark ISU® (Integrated Subsea Umbilical).
The flexible tubular conduit is stored in a basket or on a reel on the deck of the vessel and in one method is fed from the basket/reel to a vertical pipelay tower, where it is vertically aligned prior to laying the flexible tubular conduit underwater.
Guiding means in the form of an aligner, a chute or a reel is positioned on the top of the pipelay tower and used to divert the flexible tubular conduit from a horizontal path to a vertical path for laying. The guiding means generally comprises a groove, channel or gutter for receiving the flexible tubular conduit and for facilitating the diverting of the flexible tubular conduit from the horizontal path to the vertical path.
The pipelay tower further comprises tensioning means, for example pipe tensioners comprising one or more caterpillar tracks, to facilitate the feeding of the flexible tubular conduit along the required vertical path. In use, the tensioning means grip the flexible tubular conduit and help feed and deploy the flexible tubular conduit towards the seabed.
Before commencing the normal lay of the flexible tubular conduit, the first end of the flexible tubular conduit is engaged on the guiding means located on top of the pipelay tower and appropriately vertically aligned. The first end of the flexible tubular conduit is then guided along the vertical path, often referred to as the ‘firing line’ and through the tensioning means towards an opening, such a moon pool, on the deck of the vessel.
A normal procedure for getting the first end of the flexible tubular conduit onto the guiding means, and thereafter vertically aligned with the firing line involves the use of a initiation winch to lift the first end of the flexible tubular conduit onto the guiding means.
However, a flexible tubular conduit is generally provided with one or more fittings, such as an end fitting and/or stiffener, which generally have an outer diameter that is greater than the outer diameter of the flexible tubular conduit. As a result, a fitting located at the end of the flexible tubular conduit cannot easily navigate the guiding means in order to get the first end of the flexible tubular conduit vertically aligned with the firing line.
In cases where the first end of the flexible tubular conduit comprises a fitting attached thereto, the use of a deck crane or auxiliary winch is required in order to lift the fitting and position it downstream of the guiding means. This is because the fitting has a greater outer diameter than the flexible tubular conduit and as such cannot easily navigate the guiding means if just pulled by the initiation winch. Assistance of a vessel crane and men on the top of the laying tower is often required to guide the end fitting on the guiding means and to get it down the hole formed by the entrance of the upper tensioner.
U.S. Pat. No. 5,348,423 describes a method of laying a flexible tubular conduit according to the state of the art. A device is disclosed for laying flexible tubular conduits having a fitting, such as end fittings or the like, attached to the end thereof. The device comprises a main linear winch-type tensioning means for normal lowering of the flexible conduit to be laid and an auxiliary winch for lifting the fitting clear of the guiding means and into the tower when the outer diameter of the fitting is greater than the outer diameter of the conduit.
Hydrocarbons are now extracted from deeper seabed, and as a result there is a need to deploy longer lengths of flexible tubular conduit. Thus the capacity of the pipelay tower has to be increased.
To achieve this aim, larger tensioning means are required on the pipelay tower, for example moving from 1 or 2 tensioners to 3 or 4 tensioners within the tensioning means. This leads to an increase in the height of the pipelay tower as a tower having 4 tensioners will be almost twice the height of a tower having 2 tensioners.
In addition, as the flexible tubular conduit length increases, the end fitting becomes bigger and the stiffener becomes larger and longer in order to sustain the force exerted on it.
The need for bigger end fittings coupled with the increase in the height of the pipelay tower, means that methods currently known in the art are not very practical for transferring the fitting attached to the first end of the flexible tubular conduit over the guiding means. In particular, this would need a long boom vessel crane to reach the aligner reel and higher capacity crane. In addition assistance of men at this height for prolong periods of time is not recommended for safety reasons.
There is therefore a need for a transfer mechanism and method which facilitates the transfer of a fitting attached to the first end of the flexible tubular conduit over the guiding means in the deployment of longer lengths of flexible tubular conduits.